DUBLIN, Feb 4 (Reuters) - Burgers containing horse DNA have been discovered at a second plant in Ireland, the country's agriculture department said on Monday, again pointing the finger at Poland as the country of origin for the raw materials. Major food companies like Tesco and Burger King last month found that beef products supplied by an Irish firm contained horse DNA, a scandal that has hit retailers with a wave of bad publicity and left Ireland's 2 billion euro ($2.7 billion) beef industry reeling.